The voltage is obviously totally irrelevant - the MCB knows only about current. Hence 12V AC would be just as good as 230V AC. It's 12V DC I'm far less sure about.
Kind Regards, John
Periodic inspection - money well spent
- Thread starter Marvy
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Kind Regards, John
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I don't think AC/DC matters for MCBs, although it is critical for RCDs.
As you say, DC simply won't work with an RCD.
As for (the magnetic part of) MCBs, I really am not sure. I'm not sure whether a constant magnetic field would necessarily have the same effect on the trip mechanism as a corresponding 'alternating' (at least, varying, if examined for less than a cycle) magnetic field, nor whether (as with power) a given DC current would have the same magnetic effects as an AC current whose RMS value was equal to the DC current. Furthermore, as I've already mentioned, I wonder if a very large DC current might permanently magnetise some parts within the MCB, thereby possibly affecting subsequent performance.
Maybe someone knows the answers?
Kind Regards, John
It will, if they are the right sort.
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Agreed, it won't break the arc.
We're surely talking about 'the sort' found in domestic electrical installations?
Kind Regards, John
Yes. If for example there are items with variable-speed drives or inverters, there can be a high DC content in the earth leakage current. Such items are getting much more common in domestic situations - microwave ovens, washing machines, fridges etc commonly use inverters.
That's probably true, but are the RCDs usually found in domestic installations of a 'sort' which will detect DC imbalances (and with the same IΔn as for AC imbalances)? (that's a real, not rhetorical, question, because I don't know the answer!)
Not usually.
Ah - now there's a thing.
There are different sorts. Even in dwellings the correct type (A, B, AC) should be used. AC types aren't used so much elsewhere.
Not necessarily.
When breaking the supply on a fault, there's a high power supply so when the contacts open, there's the voltage and energy to initiate a spark. Basically, you've got a supply capable of putting 240V and hundreds of amps into the spark.
When testing with a low voltage test rig (I've been toying with Variac and welding set for some experiments - though that might not have the right turns ratio), there's a much lower energy available, and a much lower voltage. In principle, you only need enough volts to push the required current through a very small resistance - and I bet that's not more than a volt or two given that we don't have (in normal operation
) MCBs glowing due to the IR losses through them. So when the contacts open, there really isn't the voltage there to get an arc going.DIYnot Local
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